STREAM WATER QUALITY SIMULATION WITH REMOTE SENSING AND GIS SUPPORT

Abstract

Prediction of stream/river water quality is one of the most essential requirements for proper management of the river basin so that adequate and effective measures can be taken to keep pollutants within permissible limits. Since the concentration of the quality constituents is dependent on the quantity of flow, entry of point and non-point source pollutants, reaction kinetics, etc., it is essential to monitor and develop mathematical models for predicting water quality variables. Dissolved oxygen in rivers is one of the most important indices of river's health. Biochemical oxygen demand (BOD) and dissolved oxygen (DO) modelling has received lot of attention in the literature. Several models have been proposed in past to predict BOD and DO profiles in a stream reach. These models have gradually increased in terms of accounting for number of variables representing the decay of BOD as well as DO concentrations. For dissolved oxygen computations within a stream reach, stream reaeration coefficient is an important parameter. Numerous studies have been made to express this coefficient as a function of several variables, including mean stream velocity, shear stress velocity, bed slope, flow depth, Froude number (Fr), etc. The non-point source pollution is another important variable responsible for increasing pollutant load in a stream/river. Recognising the importance of assessing non-point source pollution in riverine system, numerous studies aimed at understanding the processes controlling nutrient concentration, fluxes in the river systems and the quantification of the nutrient loads of streams have been accomplished in the past. In view of this, in the present study attempt has been made to investigate the importance ofwater quality variables and application of different water quality models. Ageneralised BOD- DO model has been developed to estimate the BOD and DO profiles in a stream/river. The modelling approach considers the entry from nonpoint sources, effect ofmass flux, bethic oxygen demand, photosynthesis, respiration and rate constants for deoxygenation and reaeration. The developed model accounts the effect of change in discharge along with other water quality parameters. The effects of nonpoint pollutant concentration and its discharge have also been included in the model. For the limited data sets availability, the model may be simplified and transformed into water quality models developed by Streeter and Phelps (1925) and Camp (1963), which may be used to predict BOD and DO profiles along the stream. In addition to the development of generalised models for BOD and DO, the equations for estimating reaeration coefficient based on hydraulic parameters have been developed. The Froude number criteria has been employed and the results obtained using data of different streams of the world are found to be very promising. The equation for assessment of non-point source pollution entry in a river reach has been developed. To test and validate the developed model, water samples from River Kali were collected and analysed. The developed model for estimation of non-point source pollution in a stream provides very good results. Sensitivity analysis of different water quality parameters has been also done to place greater importance to more sensitive parameters. The remote sensing and Geographical Information Systems techniques have been employed for determination of reaeration coefficient, non-point source pollutants and other water quality variable